The impact of tobacco use by pregnant women on auditory processing, phonemic perception and early language in offspring will be evaluated in a cohort of 340 infants followed to 24 months postpartum. Tobacco smoking during pregnancy continues to be a public health problem with up to 20% of newborns experiencing this potentially teratogenic exposure. Although an association with growth retardation is well established, the impact on behavioral and cognitive outcomes, particularly early during development, has not been well described. This study will focus on processing of auditory information and phonemic stimuli early in development while controlling for exposure to other drugs (e.g., alcohol) and familial and environmental factors that also affect cognitive and language development. Access to a large perinatal population will allow the investigation of heavy smoking (>30 cigarettes/day) as well as determination of the dose-response relationship between levels of tobacco smoke exposure and factors affecting developmental outcome. Quantity of tobacco exposure will be measured both through maternal self-report (i.e., number of cigarettes/day) and biological measures (i.e., maternal and infant cotinine levels, a biomarker of nicotine). The sample will be stratified to allow inclusion of heavy smokers who would not be identified otherwise. Four levels of use will be included: None, 10 to 19 cigarettes/day, 20 to 29 cigarettes/day, and more than 30 cigarettes/day. Families will be recruited postnatally and followed to 24 months with laboratory visits at 6-, 15-, and 24 months. Auditory processing and phonemic perception will be operationalized using information processing methodology and psychophysiological outcome measures. Early language skills will be comprehensively evaluated using both transcriptions of natural language samples (SALT) and standardized measures of communication and parental report of language development. Tobacco smoke exposure (including postnatal environmental exposure) is predicted to negatively impact auditory and phonemic processing skills during the first 24 months and to be related to specific language delays. All analyses will control for other contributions to outcomes (i.e., Alcohol exposure, Caregiving potential, Quality of Caregiving, including language environment, Child Health and Hearing).